High-level Expression of the Human-α-interferon Gene through the Use of an Improved Baculovirus Vector in the Silkworm, Bombyx mori

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During research on the production of human α-interferon (α-IFN) in silkworms using a baculovirus, Bombyx mori nuclear polyhedrosis virus (BmNPV), as a vector, the expression of approximately 5.0×107 U/ml of α-IFN in the haemolymph was attained. In order to obtain a much higher level of expression, we paid special attention to the role of the sequence between the promoter and the translation start site of the polyhedrin gene, and found that deletion of the sequence led to depression of the expression. We therefore tried to improve the cloning vector. By means of the in vitro mutagenesis technique, a cloning vector retaining this sequence and having various restriction enzyme sites between the promoter and the terminator of the polyhedrin gene was constructed. Using this vector, a transfer vector was constructed in which the polyhedrin structural gene was replaced by human α-IFN, and recombinant viruses were prepared. When silkworms were infected with the recombinant viruses, about 1.9×108 U/ml of IFN was produced in the haemolymph of fifth instar larvae. The improvement of the vector raised the productivity of IFN approximately four-fold.